This disclosure relates to a process for preparing abrasive tips for thermal spray deposition.
The abrasive tips include coatings to enhance performance and limit heat generation and heat transfer to the blade. The abrasive tips are applied by thermal spray deposition. The blade substrate base metal surface is prepared for thermal spray deposition.
Achieving a good bond between aluminum fan blades and aluminum matrix abrasive coating is highly dependent on preparation of the base metal. The aluminum base alloy is processed with alkali cleaning methods or simply exposed to moisture in the air which creates an aluminum hydroxide layer. The aluminum hydroxide layer interferes with adhesion of the aluminum matrix thermally sprayed abrasive tip coating. That hydroxide layer cannot be removed effectively by grit blast.
The current process is to abrade the tip by hand with a ScotchBrite pad, perform a grit blast step and then use the plasma torch to further clean and heat the blade tip. This cleaning and preheat is responsible for bringing coating bond strength from less than 1 kilo-pounds per square inch (ksi) to the current level of about 6-9 ksi. There is risk that as production volume builds, the hand operation may become more variable and result in sporadic low bond strength products.
What is needed is a coating preparation process that eliminates the hand process for cleaning the blade tip and improves repeatability of the process. It would be further beneficial to reduce preparation and preheat time.